To assess physiologic effects of continuous positive airway pressure (CPAP) and positive end-expiratory pressure (PEEP) during noninvasive pressure support ventilation (PSV) in patients with acute exacerbation of chronic obstructive pulmonary disease (COPD), we measured in seven patients the breathing pattern, lung mechanics, diaphragmatic effort (PTPdi), and arterial blood gases under four conditions: (1) spontaneous breathing (SB); (2) CPAP; (3) PSV of 10 cm H2O; and (4) PSV plus PEEP (PEEP + PSV). CPAP and PEEP were set between 80 and 90% of dynamic intrinsic PEEP (PEEPidyn) measured during SB and PSV, respectively. PEEPidyn was obtained (1) from the decrease in pleural pressure (delta Ppl) preceding inspiration, and (2) subtracting the fall in gastric pressure (delta Pga) caused by relaxation of the abdominal muscles from the delta Ppl decrease. Abdominal muscle activity made PEEPidyn overestimated in almost all instances (p < 0.0001). PSV increased minute ventilation, improved gas exchange, and decreased PTPdi. PEEP added to PSV, likewise CPAP compared with SB, further significantly decreased the diaphragmatic effort (PTPdi went from 322 +/- 111 to 203 +/- 63 cm H2O.s) by counterbalancing PEEPidyn, which went from 5.4 +/- 4.0 to 3.1 +/- 2.3 cm H2O. These data support the use of low levels of PEEP (80 to 90% of PEEPidyn) to treat acute exacerbation of COPD by means of mask PSV.

Physiologic effects of positive end-expiratory pressure and mask pressure support during exacerbations of chronic obstructive pulmonary disease.

Control of abdominal muscles

Respiratory physiology in upper abdominal surgery.

Auto–positive end-expiratory pressure and dynamic hyperinflation

In normal humans during quiet breathing, expiration is mostly driven by elastic recoil of the lungs. Expiration becomes active when ventilation must be increased to meet augmented metabolic demands...

https://www.physiology.org/doi/pdf/10.1152/japplphysiol.00201.2014

Expiratory load compensation is associated with electroencephalographic premotor potentials in humans

Active expiration is produced by the abdominal muscles and the rib cage expiratory muscles. We hypothesized that the relative contribution of these two groups to expiration would affect diaphragmatic length and, hence, influence the subsequent inspiration. To address this question we measured the respiratory muscle response to expiratory threshold loading in spontaneously breathing anesthetized dogs. Prevagotomy, the increase in lung volume (functional residual capacity) and decrease in initial resting length of the diaphragm were attenuated by greater than 50% of values predicted by the passive relationships. Diaphragmatic activation (electromyogram) increased and tidal volume (VT) was preserved. Postvagotomy, effective expiratory muscle recruitment was abolished. The triangularis sterni muscle remained active, and the increase in lung volume was attenuated by less than 15% of that predicted by the passive relationship. Diaphragmatic length was shorter than predicted. VT was not restored, even though costal diaphragmatic and parasternal intercostal electromyogram increased. During expiratory threshold loading with abdominal muscles resected and vagus intact, recruitment of the rib cage expiratory muscles produced a reduction in lung volume comparable with prevagotomy; however, diaphragmatic length decreased markedly. Both the rib cage and abdominal expiratory muscles may defend lung volume; however, their combined action is important to restore diaphragmatic initial length and, accordingly, to preserve VT.

A. M. Leevers

Papers

Respiratory muscle coordination and diaphragm length during expiratory threshold loading

The Effect of Continuous Positive Airway Pressure Versus Positive End-Expiratory Pressure on the Diaphragm